A data network allows people to communicate with each other and obtain information from various sources on the network, using their respective client devices that are “on” the network. For example, a Web browser application program, running in a user's workstation or laptop computer, can connect with a Web server to download a Web page. The connection may span several intermediate nodes or hops of the network, which may include specialized computers such as routers. These devices can discover routes between the end nodes through which they can forward messages that have been broken up into packets of data. Each node may be assigned a unique or global address, such as an Internet Protocol (IP) address. The Internet is a well known global inter-network in which networks of computers are connected to each other via routers.
Computer network protocols have a layered architecture. Typically, the upper most layer includes the functionality provided by an application program, such as a Web browser. This is the layer that, at least in the end nodes, may initiate a connection between two computers over a network. Thus, for example, a user may select a desired Website on his client device. The Web browser (running in that client device) starts a procedure that results in a connection being made with a server that is associated with the selected Website. The Web browser sends the request “down” through a stack of layers referred to as an Internet protocol suite or Transport Control Protocol/Internet protocol (TCP/IP) stack. This stack of protocols is typically implemented in software at its higher layers, often as part of an operating system (OS) program running in the client device. Once the selected Website has been translated into an IP address of a Web server, the server is located over the Internet, and an appropriate connection is made with an upper layer program of a similar protocol suite implemented in the Web server.
To use the connection, the TCP/IP stack in the client device encapsulates a request message from the Web browser, in this example, a request identifying the Web page. The message may be encapsulated more than once, by several vertical layers on its way down in the protocol stack, including a network access layer. It finally arrives at the lowest layer of the client device, namely the physical layer (which is typically deemed to be a part of the network access layer).
The physical layer includes hardware, and may also include software, that is responsible for delivering the encapsulated message to the next device in the network. For example, Ethernet is a family of frame-based computer networking technologies for local area networks (LANs), which defines a number of wiring and signaling standards for its waveguide-based (e.g., wire; optical fiber) physical layer. Ethernet also defines several means of network access at what is referred to as the media access control (MAC) or data link layer, just above the physical layer. In recent years, a wireless LAN technology standardized by IEEE 802.11, also referred to as Wi-Fi, has been used in addition to or instead of Ethernet in many installations. Currently, many laptop computers are shipped with Wi-Fi capability, in addition to an Ethernet port. The Wi-Fi capability links the client device to a nearby base station or wireless router. An Ethernet cable links the client device to a router or an adapter (such as a DSL modem).
After leaving the client device and then making its way through one or more hops in the network, the message from the Web browser arrives in the Web server, and is passed “up” the protocol stack in the Web server to a program that is deemed a peer of the Web browser. The peer program may then respond to the message, by causing the data for the requested Web page to be collected and sent back to the client device through the existing network connection. The data is broken up into multiple messages or packets, and is sent in a manner analogous to how the request message was sent.
Most recently, conventional cellular telephone handsets have been enhanced with the capability of Web browsing and email access for the subscriber, in addition to providing two-way voice communications. For instance, a digital mobile phone technology (including a special physical layer) that allows for improved data rate and reliability to support a packet switched Internet connection, has been deployed, referred to as Enhanced Data rates for GSM Evolution (EDGE). Such cellular phone handsets are advertised as being able to run high speed data applications such as video services. There is also the upcoming third generation (3G) mobile phone technology known as Universal Mobile Telecommunications System (UMTS) that allows the client device to communicate with a base station using a W-CDMA air interface (in the physical layer).